Goals for the current year include initiation of experiments designed to elucidate the role of phosphorylation of basic protein in the assembly of myelin. Kinetics of addition and turnover of phosphorous on the myelin basic protein will be studied in young and old animals using (32P)- and (33P)phosphate. The flow (order of appearance) of radio-active phosphorous through myelin subfractions (myelin from young animals can be separated on the basis of density, the denser fractions being on the route to buoyant "mature" myelin) will be determined. Metabolism of myelin in rats exposed to triethyl tin will be studied to help elucidate the mechanisms by which myelin is destroyed and, in the recovery stage, what process leads to formation of new myelin. Another phase of the proposed work deals with further characterization of axonal transport of lipids and proteins. Following injection into the region of neuronal cell bodies, immunoprecipitation methods will be used to characterize individual radioactive proteins arriving at the nerve ending.